1. Field of the Invention
The invention relates to an apparatus for crucible-free zone melting of a semiconductor rod including an annular induction heating cole adapted to annularly encompass a zone of the rod and upon activation to produce an annular melt zone on such rod and somewhat more particularly to such an apparatus wherein the heating coil is parallelly connected to a capacitance and electrical current conduits couple the coil and the capacitance to the output circuit of a high frequency generator.
2. Prior Art
U.S. Pat. No. 3,271,551 (which corresponds to German Pat. No. 1,198,324) describes an apparatus for crucible-free zone melting of a semiconductor rod which has a heating circuit comprised of an annular induction heating coil adapted to annularly encompass the semiconductor rod and upon activation to produce an annular melt zone on such rod and a parallelly connected capacitance which is coupled via electric current conduits to an output circuit of a high frequency generator.
In this type of device, the tuning capacitors for the required capacitance are in the form of Teflon (a registered trademark for polytetrafluoroethylene) capacitors. These Teflon capacitors are positioned directly at the location of the induction heating coil in the zone melting chamber of a gas-impermeable (vacuum-tight) housing. However, at high HF power, such as required for non-crucible zone melting of silicon rods having an increased diameter, for example, greater than 50 mm, the utility of such capacitors is limited since they become extremely subject ot disturbances or destruction.